Multiple pass optical matrix system

ABSTRACT

A multiple pass optical matrix system comprises two main and one additional objective mirrors arranged on a mount. The mount is mechanically connected with means for rotation of the mount about axes perpendicular and parallel to the image matrix row. The main and auxiliary field mirrors are placed opposite the mount along the longitudinal axis of the system.

FIELD OF THE INVENTION

This invention relates to optical instruments and, in particular, tomultiple pass optical matrix systems.

BACKGROUND OF THE INVENTION

All modern infrared spectrophotometers comprise optical multiple passlong-path systems. However, we are now witnessing the advent of newspectroscopy based on the use of high-intensity lasers and superhighresolution laser semiconductor spectrometers. In these conditions,conventional multiple pass optical systems utilizing the classical Whiteabsorption cells are definitely obsolete since they cannot provide alarge enough number of passes in the system.

Multiple pass optical systems showing great promise at the present stageof development are based on image matrices on arrays. But the existingmatric systems are extremely complicated and unreliable.

Known in the art is a multiple pass optical matrix system (cf., forexample, Journal of the Optical Society of America, 66, No. 5, May 1976,John U. White, Very Long Optical Paths in Air, pp. 411-416) comprisingthree objective mirrors arranged at the input and output of the laserbeam, two main field mirrors having the radius of curvature equal tothat of the objective mirrors and positioned at a distance equal to theradius of curvature of the latter, and also two diagonal mirrors havingthe total radius of curvature equal to the radius of curvature of anindividual field mirror, arranged at an angle close to a right angle andadjoining one of the main field mirrors. In this system, each fieldmirror is individually mounted and can be rotated.

But this system is deficient in that the objective mirrors areindividually mounted and rotated and the errors accumulate with thenumber of passes. The system, therefore, is extremely unstable, which isparticularly felt if the number of passes is large.

Besides, the system comprises diagonal field mirrors operating at largeincident angles, which results in greater astigmatism and, consequently,larger sizes of images.

One more deficiency consists in that the diagonal field mirrors produceadditional reflecting surfaces impairing the translusency of the system.

This system is extremely complicated in design and adjustment, whichaffects its operational characteristics.

And, finally, the system can only operate with a coherent radiationsource whose beam divergence is very small, which is a seriouslimitation to its application field.

Also known in the art is a multiple pass optical matrix system (cf., forexample, P. L. Hanst, Advances in Environmental Science and Technology,vol. II, ed. by J. N. Pitts and R. L. Metcalf, Wiley, NY, 1971, pp.160-165) comprising at least four objective mirrors, at least four fieldmirrors whose radii of curvature are equal to those of the objectivemirrors, and which are arranged at a distance equal to the radius ofcurvature from said objective mirrors on the side of the entrance andexit apertures, and a means for coupling light beams out of the cell. Inthis system objective mirrors have individual adjustments, and onemirror can be rotated.

But this system is deficient in that individually adjustable objectivemirrors and one angularly displacable mirror to change the number ofpasses can be the cause of error accumulation. The system is notvibration proof. The recommendation to cast the mirror array in epoxycement produces a single purpose system which cannot be adjusted for anyother application.

Besides, in this system each field mirror produces only one row ofintermediate images, which is a limitation to the measuring range. Toexpand the measuring range by increasing the number of passes, moreobjective and field mirrors should be added, the total number of mirrorsmust be a multiple of four. Thus, a system for 220 passes and 10 rows ofimages in the matrix should have a total of 20 objective and fieldmirrors. The system becomes extremely complicated to operate and,consequently, unreliable.

Also known in the art is a multiple pass optical matrix system (cf., forexample, U.S. Pat. No. 3,726,598, Cl. G OIJ 3.02, Apr. 10, 1973) whereinthe radiation flux from an illumination source enters through an inletwindow of the cell housing to hit one of the two rigidly secured mainobjective mirrors having the same radii of curvature and mechanicallyconnected to a mount which is secured to a means for rotating saidmirrors about an axis perpendicular to the row of images on the matrix,and further hits a main field mirror whose radius of cruvature is equalto that of the main objective mirror and which is arranged along thelongitudinal axis of the system at a distance equal to the radius ofcurvature of the main objective mirrors, wherefrom the radiation flux isdirected to another main objective mirror, is reflected therefrom to themain field mirror, and is once more directed to the first main objectivemirror, and in the last pass leaves the system through the exit window.

This system is deficient in that the image matrix on the main fieldmirror has only two rows, thus limiting the number of passes and,therefore, the length of the optical path which can be achieved in thissystem.

SUMMARY OF THE INVENTION

This invention is to provide a multiple pass optical matrix systemfeaturing such additional elements which make it possible to increasethe number of intermediate images on the field mirror.

There is provided a multiple pass optical matrix system wherein theradiation flux from an illumination source comes through an entrancewindow of a housing and strikes one of the two rigidly secured mainobjective mirrors having the same radii of curvature, which aremechanically secured to a mount which is connected to a means forrotating said mirrors about an axis perpendicular to the row of imageson an image matrix, and further falls on a main field mirror whoseradius of curvature is equal to that of the main objective mirrors,which is arranged along the longitudinal axis of the system at adistance equal to the radius of curvature of the main objective mirrorsand from which the radiation flux is directed to another main objectivemirror, is reflected therefrom to the main field mirror, and from thereis directed to the first main objective mirror, and, in the last pass,leaves the system through the exit window of the housing, and which,according to the invention, comprises an additional objective mirrorhaving same radius of curvature, which is mechanically secured to themount, a means for rotation about an axis parallel to the image matrixrow, which is connected to the mount, and an auxiliary field mirrorhaving the same radius of curvature, which is arranged on the same axisas the entrance and exit windows and close to the main field mirror.

Advisably, in the proposed matrix system, the mount should be made oftwo parts, one part carrying two main objective mirrors and connected tothe means for rotation about an axis parallel to the image matrix row,and the other part carrying the additional field mirror.

Desirably, the proposed system should comprise one more additionalobjective mirror having the same radius of curvature, which ismechanically connected to the mount and rigidly secured to theadditional objective mirror, the center of curvature of the main fieldmirror being positioned in the center of symmetry of the main andadditional objective mirrors, while the center of curvature of theauxiliary field mirror is located in the center of symmetry between thefirst main objective mirror and respective additional objective mirrors.

Preferably, in the proposed matrix system, the mount should be made as aplate whereon the main and additional objective mirrors are installed.

This invention permits a substantial increase in the number of rows inthe image matrix and, consequently, makes the optical path much longer.

In addition, this invention makes it possible to obtain a doublesuperposition of images in the matrix, which can also increase theoptical path.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in more detail with reference tospecific embodiments thereof and to the accompanying drawings, wherein:

FIG. 1 shows a perspective view of a multiple pass optical matrix systemfeaturing three objective mirrors, according to the invention;

FIG. 2 shows a longitudinal sectional view of an absorption cellcontaing the multiple optical matrix system of FIG. 1, according to theinvention;

FIG. 3 shows a cross sectional view taken along line III--III of FIG. 2and turned by 180°, according to the invention;

FIG. 4 shows a cross sectional view taken along line IV--IV of FIG. 2,according to the invention;

FIG. 5 shows a longitudinal sectional view of an absorption cellcontaining a multiple pass optical matrix system having four objectivemirrors, according to the invention;

FIG. 6 shows a cross sectional view taken along line VI--VI of FIG. 5and turned by 180°, according to the invention;

FIG. 7 shows a view taken along arrow A of FIG. 5, the main andadditional field mirrors being enlarged, according to the invention;

FIG. 8 shows a schematic view of a mount and three square objectivemirrors arranged in a row, according to the invention;

FIG. 9 shows a schematic view of a mount and four square objectivemirrors arranged in a row, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In a multiple pass optical matrix system according to the invention aradiation flux 1 (FIG. 1) from a radiation source (not shown) issupplied through an entrance opening 2 made in a lid 3 of a housing 4(FIG. 2) of a cell 5, and falls on a main objective mirror 6 (FIGS. 1,2, 3). The objective mirror 6 is placed in the path of the flux 1 on aplate 7 of a mount 8. A main objective mirror 9 is located on the plate7 next to the objective mirror 6. The plate 7 is connected to a shapedstrip 10 by a pivot shaft (rod 11) of a means 12 for rotation of theplate 7 about an axis 13. The means 12 also comprises a screw 14 with ahand nut 15. The screw 14 extends through a cover 16 of the housing 4and butts up against the plate 7. The strip 10 is secured to across-piece 17 of the mount 8, which can be tilted in relation to ahorizontal axis 18 on a support shaft (support roller 19) of a means 20for rotation about the axis 18, which extends through the base of thecross-piece 17 and openings in the housing 4. The means 20 alsocomprises a hand nut 21 secured to the roller 19. An additionalobjective mirror 22 is installed on the cross-piece 17. A spring 23 isinserted between the plate 7 and the cover 16. A main field mirror 24(FIGS. 1, 2 and 4) is placed in the path of the flux 1 reflected fromthe objective mirror 6. Beneath the entrance opening 2 and next to thefield mirror 24 is placed an auxiliary field mirror 25. All objectivemirrors 6,9,22 and field mirrors 24 and 25 have the same radius ofcurvature. Digits from 1 to 14 on the field mirrors 24 and 25 are toindicate the sequence of images forming a rectangular image matrix 26whose rows are perpendicular to the axis 13 and parallel to the axis 18.An exit opening 27 is provided in the cover 3 on the vertical axis ofthe entrance opening 2 and above the field mirror 25 for the radiationflux 1 to leave the system in the last pass. The openings 2 and 27 areprovided with windows 28 transparent to the radiation flux 1. Thecenters of curvature of the objective mirrors 6 and 9 are indicated byrespective points 28 and 30 on the field mirror 24, and of the objectivemirror 22 by a point 31 on the field mirror 25. The center of curvatureof the field mirror 24 is located in the center of symmetry of theobjective mirrors 6 and 9 and is indicated by a point 32. The center ofcurvature of the field mirror 25 is indicated by a point 33.

In an alternative embodiment of a multiple pass optical matrix system, amount 34 (FIG. 5) comprises a plate 35 (FIGS. 5 and 6) and a ring 36connected by a pivot shaft (pins 37) of the means 12. The ring 36 issecured to a support shaft (pins 38) of the means 20. Pins 38 extendthrough holes in the housing 4. Mounted on the plate 35 are two mainobjective mirrors 39 and 40 and two additional objective mirrors 41 and42. A plate spring 43 is inserted between the plate 35 and cover 16. Thecenter of curvature of the main field mirror 24 is located in the centerof symmetry of the objective mirrors 39,40,41 and 42, and is indicatedby a point 44. The center of curvature of the auxiliary field mirror 25is located between the objective mirrors 39 and 41, in their center ofsymmetry and indicated by a point 45. The objective mirrors 39,40, 41and 42 and field mirrors 24 and 25 have the same radius of curvature.

Referring to FIG. 7, a rectangular image matrix 46 is provided for 90passes of the radiation flux 1, the sequence of images being indicatedby digits from 1 to 44. The matrix rows are perpendicular to the axis 13and parallel to the axis 18. The centers of curvature of the pairs ofobjective mirrors 39,40 and 41, 42 are located on the surface of thefield mirror 24 and indicated, respectively, by points 47, 48, 49 and50.

In one more embodiment of a multiple pass optical matrix system, a mount51 (FIG. 8) comprises a bracket 52 with a plate 53 being placed insidesaid bracket 52. A means 54 for rotation about the axis 13 comprises asleeve 55 and a pin 56 extending through a hole in the bracket 52, andthe sleeve 55. The plate 53 is fit on the pin 56. Main rectangularobjective mirrors 57 and 58 are located on the plate 53. A cheek-piece59 is secured to the face of the bracket 52 to carry an additionalrectangular objective mirror 60. The objective mirrors 57, 58 and 60 arearranged in one line on the horizontal axis 18. A means 61 for rotationabout the axis 18 comprises pins 62 and 63 secured to the bracket 52 andplaced in sleeves 64 and 65 repectively. The center of curvature of thefield mirror 24 (FIG. 1) is situated in the center of symmetry ofobjective mirrors 57 and 58 and designated by a point 66 (FIG. 8). Thecenter of curvature of the field mirror 25 (FIG. 1) is located betweenthe objective mirrors 57 and 60 (FIG. 8) and designated by a point 67.

And, finally, in still another embodiment of a multiple pass opticalmatrix system, a mount 68 (FIG. 9) comprises a bracket 69 and sleeves 70and 71 made integral therewith. A plate 72 is located inside the bracket69 and carries two main rectangular objective mirrors 73 and 74 and twoadditional rectangular objective mirrors 75 and 76 arranged in one rowalong the horizontal axis 18. The pin 56 with the sleeve 55 of the means54 is secured to the bracket 69. The pins 62 and 63 are located,respectively, in the sleeves 70 and 71. The center of curvature of thefield mirror 24 (FIG. 7) is located in the center of symmetry of theobjective mirrors 73, 74 and 75, 76 (FIG. 9) and designated by a point77. The center of curvature of the field mirror 25 (FIG. 1) is locatedin the center of symmetry of the objective mirrors 73 and 75 anddesignated by a point 78.

A multiple pass optical matrix system of FIGS. 1, 2, 3 and 4 operates asfollows.

The radiation flux 1 passes through the entrance opening 2 and falls onthe main objective mirror 6 which produces the first intermediate imageof the entrance opening 2 on the surface of the field mirror 24 (digit 1encircled by a dotted line). The plate 7 of the mount 8 and, therefore,the objective mirrors 6 and 9 can be turned by the hand nuts 15 and 21,respectively, of the means 12 and rotated about the axis 13perpendicular to the rows of the image matrix 26; the means 20 forrotating the plate 7 about the axis 18 parallel to the rows of the imagematrix 26. The tilting angle of the objective mirrors 6 and 9 dictatesthe distance from the entrance opening 2 to its first image in thehorizontal row of the image matrix 26 on the main field mirror 24 (digit1 encircled by a dotted line). The tilt of the mount 8 together with theobjective mirrors 6,9 and 22 dictates the downward vertical displacementof the image. After the first image is formed, the radiation flux isreflected from the field mirror 24 to the objective mirror 9 whichproduces a second image (digit 2 encircled by a dotted line). The mainobjective mirrors 6 and 9 alternately focus the images of the entranceopening 2 on the field mirror 24 with a certain displacement until tworows of images are formed (digits 6,4,2 encircled by dotted lines formthe first row, while digits 1,3,5--the second row) and the image findsitself on the field mirror 25 (digit 7 encircled by a dotted line). Theradiation flux reflected from the field mirror 25 falls on the objectivemirror 22 which returns it to the field mirror 25 with a verticaldisplacement. The radiation flux 1 is further directed to the objectivemirror 6 and a next pair of rows is formed as described above in theimage matrix 26 and so on until the last image comes to the exit opening27.

During the simultaneous rotation of the objective mirrors 6 and 9, theircenters of curvature (points 29 and 30) slide over the surface of thefield mirror 24, the distance between them remains unchanged. When themount 8 is tilted, the objective mirrors 6 and 9 are displacedvertically. The vertical interval between the line along which thecenters of curvature (points 29 and 30) of the objective mirrors 6 and 9situated and the center of curvature (point 31) of the objective mirror22 remains permanent. Consequently, the number of passes of theradiation flux 1 can be changed.

The adjustable number of passes of the flux 1 through the system ofthree objective mirrors 6, 9, and 22 produces series of numberssatisfying specific relations depending on the number of rows andcolumns in the matrix 26. The number of passes of the flux 1 can beobtained from the following relation:

    N=2mn-2,

where

N is the number of passes

m is the number of rows making up a series of natural numbers 2,4,6,8,10. . . ;

n is the number of columns making up a series of natural numbers1,2,3,4,5 . . .

A multiple pass optical matrix system of FIGS. 4,5 and 7 operates asfollows.

The radiation flux 1, similarly to the above embodiment, passes throughthe entrance opening 2 to fall onto the objective 39 which produces afirst intermediate image of the entrance opening 2 on the surface of thefield mirror 24 (digit 1 and digit 17 encircled together by a dottedline). The hand nut 15 of the means 12 is used to turn the plate 35 ofthe mount 34 together with the main objective mirrors 39 and 40 andadditional objective mirrors 41 and 42. The plate 35 is turned about theaxis 18 parallel to the rows of the image matrix 46 by the hand nut 21of the means 20. The fixed turn of the plate 35 determines the distancefrom the entrance opening 2 to its first image in the horizontal row ofthe image matrix 46 on the field mirror 24. The fixed tilt of the plate35 determines the downward vertical displacement of this image. Afterthe first image is formed, the flux 1 is reflected from the field mirror24 to the objective mirror 40 which produces a second image (digit 2encircled by a dotted line). The objective mirrors 39 and 40 alternatelyfocus the image of the entrance opening 2 on the field mirror 24 with acertain displacement until two rows of images (digits 8,6,4,2 encircledby dotted lines form the first row, and digits 1,3, 5,7 encircled bydotted lines for the second row) are formed and the last image findsitself on the auxiliary field mirror 25 (digit 9 encircled by a dottedline). The radiation flux 1 reflected from the field mirror 25 isdirected to the objective mirror 41. The objective mirrors 41 and 42alternately focus images and produce two new rows of images on the fieldmirror 24, and the last image is again on the field mirror 25 (digit 18encircled by a dotted line). Then the objective mirrors 39 and 40 areagain engaged. This goes on until the last image comes to the exitopening 27.

When the plate 35 turns, the centers of curvature (points 47,48,49,50)of the objective mirrors 39, 40,41 and 42 slide over the surface of thefield mirror 24, the distance between said centers of curvature remainspermanent. When the plate 35 tilts, they are displaced vertically buttheir mutual arrangement remains unchanged.

Since the centers of curvature (points 47,48, 49 and 50) of theobjective mirrors 39,40,41 and 42 are spaced apart vertically with acertain displacement, a double superposition of images is produced inthe matrix 46 as has been described above, but the arragnement principleremains unchanged.

The number of passes of the radiation flux 1 in the system comprisingfour objective mirrors 39,40,41 and 42 can be obtained from therelation:

    N=(4n-2)(m-1).

Overlapping of images in the matrix 46 is produced when m=4 and n=2.

In accordance with the invention, this matrix system can practicallydouble the number of passes of the flux 1 without resorting to largerfield mirrors 24 and 25.

A multiple pass optical matrix system of FIGS. 1, 4 and 8 operates asfollows.

The radiation flux 1, as described above, falls at first on theobjective mirror 57. The objective mirrors 57 and 58 produce two rows ofimages on the field mirror 24. The flux 1 reflected from the fieldmirror 25 falls on the objective mirror 60 which brings it back with avertical displacement. A next pair of image raws is formed then and soon, until the last image leaves the system.

A multiple pass optical matrix system of FIGS. 1, 7 and 9 operates asfollows.

The radiation flux, as described above, at first comes to the objectivemirror 73. The objective mirrors 73 and 74 produce two rows of images onthe field mirror 24. The flux 1 is reflected from the field mirror 25and is directed to the objective mirrors 75 and 76 which produce thenext pair of image rows and so on, until the last image leaves thesystem.

According to the invention the objective mirrors 60,57 and 58 (FIG. 8)and objective mirrors 75,73,74 and 76 (FIG. 9) are arranged in a lineand the system is easy and convenient to arrange.

The system according to the invention is simple and, consequently,reliable.

One more important feature of the invention consists in thereproducibility of the system and a very low level of aberrationdistortions.

INDUSTRIAL APPLICABILITY

This invention can be used to determine the atmosphere compositionincluding microconcentrations and pollutants.

Another application of the present invention consists in studying theair transparency on open routes which can be many kilometers long.

This invention can be an important tool for high and superhighresolution spectroscopy.

This invention can also be used as a noise-free variable optical delayline for resolution of very fast elementary processes, for calibrationand synchronization of high-speed recording devices for investigatingtransient processes.

This invention can be successfully used in space explorations forinterpretation of the atmosphere spectra of distant planets.

We claim:
 1. A multiple pass optical matrix system wherein a radiationflux from an illuminating source passes through an entrance opening of ahousing to one of two rigidly secured together main objective mirrorshaving equal radii of curvature and mechanically connected to a mount,the mount being attached to a means for rotating the main objectivemirrors about an axis perpendicular to the rows of an image matrix, theradiation flux then passes to a main field mirror having a radius ofcurvature equal to the radii of curvature of main objective mirrors andbeing arranged along the longitudinal axis of the system at a distanceequal to the radius of curvature of the main objective mirrors, the mainfield mirror directs the radiation flux to another main objectivemirror, and the radiation flux is reflected therefrom to the main fieldmirror, and from there to the first objective mirror, and, in the lastpass, leaves the system through an exit opening of the housing, whereinthe improvement comprises an additional objective mirror having the sameradius of curvature and mechanically connected to the mount; a means forrotating said additional objective mirror about an axis parallel to therow of the image matrix, said rotating means connected with the mount;and an auxiliary field mirror having the same radius of curvature andplaced next to the main field mirror.
 2. A system according to claim 1,wherein the mount is made up of two parts, one part carries the two mainobjective mirrors and is connected with the means for rotating theobjective mirrors about an axis parallel to the row of image matrix anda second part of the mount carries the additional objective mirror.
 3. Asystem according to claim 1, wherein the system further comprises anadditional objective mirror having the same radius of curvature,mechanically connected to the mount and rigidly secured to theadditional objective mirror, a center of curvature of the main fieldmirror being situated in a center of symmetry of the main and additionalobjective mirrors and a center of curvature of the axuiliary fieldmirror is located in a center of symmetry between the first mainobjective mirror and the respective additional objective mirror.
 4. Asystem according to claim 3, wherein the mount is made as a plate andthe main and additional objective mirrors are installed upon the plate.